The list is large, but I will enumerate some of the most important pieces: The good plan is basically a shorter version of the bad plan one in which no indexes were considered. No dynamic sampling appears. Disclaimer All my postings reflect my own views. To get a trace file split into pieces, change the trace file identifier. Written by Carlos Sierra May 8, at 5:
Optimizer debug trace event, trace file. The scripts in this blog post can let you efficiently, systematically, and quickly collect trace files on a SQL statement. The second trace file is not there because I did not force a hard parse on the second statement execution. To get a trace file split into pieces, change the trace file identifier. Written by Carlos Sierra May 8, at 5: Click here to read the entire case study. Directly related to the cluster factor below.
I could have also forced a hard parse by placing the random string in a comment:.
Here is a one-line script for starting the trace Fill in your details below or click an icon to caase in: It is available at Amazon and many other retailers.
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Oracle Database – Trace File to understand the Optimizer (CBO) [Gerardnico]
This script sets the tracefile identifier to a random string. So lets enjoy it: I tried to create a small filss for a better understanding of this event dump, following script creates a table fikes a primary key and unique key constraints and the CBO decides to use the unique key constraint over primary key; Code listing It was a real challenge packaging so much info in only two days, but I am very pleased with the result. The trace file can be big if you are working on lots of joined tables since every possible combination will be dumped to the trace file.
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Oracle Database – Trace File 10053 to understand the Optimizer (CBO)
Execution Plan before and after Plan stability? The demonstration is a throwaway example. We will compare both traces at some points, but mainly focus on how the costs were computed for the bad plan.
Filees Clustering factor of this index; a measure of how sorted a base table is with respect to this index.
Take for example this: Along the way, we will also gain insight into how the Cost Based Optimizer CBO arrives at the cost for a query and, ultimately, how it arrives at the execution plan.
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To get trace output, is necessary to force a hard parse. The analysis of the bytes difference follows. In conclusion, whether dynamic stats or gathered stats were used, the resulting plan was the same. This script displays the trace file name.
Analyzing Trace Files. The simplified dynamic sampling query is: Email required Address never made public. You are commenting using your Twitter account.
It is also important to point out that the algorithms used by the CBO to estimate the cost of a query may change from version to version as well. Maybe you are hitting a CBO bug and this trace file offers best for you to show Oracle support something unexpected happening. The second trace file is not there because I cawe not force a hard parse on the second statement execution.
Scripts for trace 10053
The good plan is basically a shorter version of the bad plan one in which no indexes were considered. You are commenting using your Google account. Notice that there are two trace files this time, one for each statement.
Oracle Performance — H. You are commenting using your Google account. The intentions casse always good, but the process is painful and time consuming.
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